This collaborative study is an extension of work performed as part of Dr. Nair's NIH grant (DK41973) by Dr. Moller during a one-year sabbatical in Dr. Nair's laboratory. Dr. Moller has a collection of patients with growth hormone deficiency in whom they replaced growth hormone (a routine therapeutic approach in Europe, although not universally accepted in the United States). These patients provide a valuable opportunity to determine the effect of replacement of growth hormone on muscle protein synthesis. The study will provide substantial information about the need of replacing growth hormone deficiency. Sample analysis is performed in the Biomedical Mass Spectrometry Core Laboratory.